In the fabrication of devices, e.g., semiconductor devices or magnetic bubble devices, it is generally necessary to form on a substrate a metallic or metal oxide region having a specific spatial pattern and location. (A substrate is a mechanically stable body including either a bulk material upon which a device is to be formed, e.g., bulk silicon, or including the bulk material and other regions, e.g., metal regions, insulating regions, or semiconductor regions, formed during the processing of the device.) The positioning and patterning of metal or metal oxide regions are often accomplished by a lithographic process. In this process, a mask is used to image energy into the desired two-dimensional pattern on the substrate surface coated with an energy-sensitive resist material. The mask is placed in contact with or in close spatial relation to the substrate. Alternatively, the mask pattern is projected onto the substrate.
After the selective exposure, a procedure is employed to remove portions of the resist and thus to expose corresponding portions of the substrate. For example, a solvent or energetic entities from a plasma are utilized to accomplish the desired removal. The resulting patterned energy-sensitive material, i.e., resist, is employable as a processing mask for a variety of procedures, such as selective doping, etching, or oxidizing the exposed substrate. Alternatively, in a procedure denominated lift-off, a metal is deposited on the pattern and thus also onto the exposed portions of the substrate. The resist is then totally removed, for example, with a suitable solvent, leaving a patterned metal region.
Although the formation of metal or metal oxide patterns in device fabrication is most commonly employed for producing, respectively, electrically conductive or insulating regions in a device, other application also require the selective deposition of a metal or metal oxide region. For example, the mask utilized in the previously described patterning procedure generally comprises a patterned metal or metal oxide film, such as a chromium, chromium oxide, or nickel film in the case of a photomask, or a gold film in the case of an X-ray mask, generally having a thickness of approximately 500 to 1000 Angstroms in the former case and 3500 to 8000 Angstroms in the latter. The mask is generally formed on a base which is transparent to the incident radiation, such as a quartz or glass base having a thickness of 0.06 to 0.09 inches for the photomask, and a dielectric film, e.g., a boron nitride/polyimide composite film, in the X-ray case. The mask is typically manufactured by depositing a thin film of the metal or metal oxide onto the entire surface of a substrate. This film is then coated with a resist which is sequentially exposed, developed, and the film selectively removed in the exposed area by etching, leaving the desired pattern. (See D. J. Elliott, Integrated Circuit Fabrication Technology, McGraw-Hill, New York, 1982, and D. K. Atwood et al, Proceedings of the SPIE, Vol. 471, Santa Clara, March 1984, page 127, for a description of the fabrication of photo and X-ray masks, respectively.)
In the manufacture of a mask, transparent defects such as pinholes or missing portions of metal or metal oxide film often occur. These defects in turn cause defects in the integrated circuits or other devices produced when using such masks. Since the manufacture of masks is generally a time-consuming and relatively expensive operation, it is often desirable to repair a defective mask by selectively depositing an opaque metal or metal oxide film on the undesired transparent region. (Transparent and opaque are terms employed in relation to the exposing radiation.)
Techniques for the selected deposition of metals or metal oxides have also been used in the repair of masks, but have several disadvantages in this application. For example, the resist which is applied and developed to expose the transparent mask regions may itself develop pinholes, thus causing the metallic film to be ultimately deposited in areas other than undesirable transparent regions. This unwanted deposition creates what is known as opaque defects on the transparent substrate that then need to be corrected. Additionally, the metallic film deposited on the mask may have poor adhesion and thus be removed during the concomitant removal of the resist material. (The degree of adhesion required for photomasks is much higher than for X-ray masks because of the scrubbing and cleaning procedures associated with the use of the photomask.) Finally, such a technique requires many steps and is time-consuming.
Laser-writing procedures have been considered for the repair of photomasks because they are not only less time-consuming but also offer the possibility of producing a film in only the defect areas. For example, as described in U.S. Pat. No. 4,340,654, dated Jul. 20, 1982, laser energy was utilized to fuse an opaque coating material to a photomask substrate surface at the location of the transparent defect. Unfortunately, fusion causes physical and optical damage to the substrate and deposited coating material. Thus, if too large an area or the wrong area of the mask substrate is exposed, it would be impossible to correct the newly formed opaque area with standard repair techniques since the underlying substrate is now damaged or removed.
Another method depending upon the use of a directed laser beam is described in U.S. Pat. No. 4,444,801, dated Apr. 24, 1984. This method utilizes laser-induced metal deposition and provides that an organometallic complex solution be applied either to the entire surface of the photomask having transparent defects or only to the transparent defect portion and its periphery. Each transparent defect is then exposed to visible or ultraviolet light to induce deposition of a metal into the transparent defect, thereby correcting the defect on the photomask pattern. However, the formed metal region is not adherent and requires a protective covering to maintain its integrity.
Because the opaque pattern in X-ray masks is formed on an extremely thin film, repair of pattern defects is quite difficult. For instance, because it is not possible to lift off a metal region thick enough to be opaque to X-rays, the previously described lift-off techniques are not applicable. J. N. Randall et al, "Repair of X-ray Lithography Masks Using UV Laser Photodeposition," Journal of Vacuum Science and Technology B, Vol. 3, No. 1, Jan./Feb. 1985, have suggested repairing masks by flowing an organometallic gaseous material, e.g., dimethyl cadmium and tetraethyl lead, over the mask surface and irradiating the defect areas of the mask with laser radiation. Thus, deposition from the gas phase onto the defected portion of the mask is induced. However, this deposition is extremely inefficient and requires special handling techniques.